Controlled suspension polymerization



Aug. 13, 1963 P. D. MEEK ETAL CONTROLLED SUSPENSION POLYMERIZATION 2 Sheets-Sheet 1 Filed Aug. 3, 1959 JOSEPH R SNVDER B/RT ALL/SON GEORGE GR/MES Aug. 13, 1963 Filed Aug. 3, 1959 P. D. MEEK ETAL CONTROLLED SUSPENSION POLYMERIZATION 2 Sheets-s img. 2

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INV ENTORS PAUL D. MEEK JOSEPH R. SNYDER B/RT ALL/SON GEORGE GR/ME` TIME /N HOURJ:`

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ATTORNEY United States Patent Office s 3,100,763 s s CONTROLLED SUSPENSION POLYMERIZATION n Paul D'.- Meek, Joseph R. Snyder, Bin Aureon,- end George Grimes, Big Spring, Tex., assignors to` Cosden' Petroleum Corporation, Big Spring, Tex., a corporation of Delaware.. y

Filed Aug.`3, 1959Se13HNo. 831,269 3 Claims. (Cl. Zoll-93.5)

s This invention relates to suspension' polymerization and provides a controlled proceduremore reliable,v to elect a` satisfactory suspension polymer bead product by `a,icont'inuous pil-I control through all phases of the reaction. Despite operation of a suspension polymer` system in the usual ranges of Vnecessary components, a large percentage of failures occur which we have found, according' to fthe present invention, can be prevented by continuous p-I-I control.- s l f p s s In operation of a *suspension` system to p roducepolymer ready iiowable granulargbead-like formby agita-t ing polymerizable reaction componentsasl a suspension in Water, numerous lcontrol elementsrhave been proposed and ,are followed las common, if not standard Aprocedure l 2 It is also useful inI the suspnsionpolymerization of vinyl chloride, vinyl acetate, yinyl prop ionate, vinylidene chloride, the lower esters, for example methyier ethyl esters ofra'c'rylic or niethacrylicpaoids, acrylonitrile, butadiene, chloroprene and mixturesH of such ethylenic'ally unsaturatedmono'mers.; It isfuseful fo'r polymerizng a suspension of3 such monomers o 'r mixtures thereof, asa monomer solution of other polymers, suchyas latices of natural and syntheticwrubbers, suchlas a monomer solution of in this art. Each' control factor appears usually toehave afdesirafble effecten theA successful production of polymer in ibead forni from liquidtpolymerizablesubstance suspended `as "nely droplets by, agitation in"water. For instancekdiicultly soluble phosphates of the group, calcium, 4bariumand magnesium, have been proposed for their function1 as dispersing agents and suspension sta'- ybilizers to inhibit the intermediate or ultimate agglomeraftionloftheV particles of pt )lymerizable substance 4 'IIhese phosphates have been suggested for use in lim-` ited range ofV particle size and in quantity ratio` with respect toother componentsoff` theA suspension system. For instance,L a common particle size range is a submcron', defined as 0.2 Lto 0.005 micron, butaccordng to a preferred method of forming the particles described below, the phosphate particles may be of even smaller size. The quantity ofphosph'ate hasY been suggested to ranger from about 0.005 to )about 5% of the suspensionand` mostvusually rangesin the practice of the art, from about, 0.1M to 3%. They have also been proposed [to be used Withjvarious surface activeagents, typically anionic agents in quantity ranging from .005 to,2% by weight of the suspension system, as well, as monomer soluble dispersing agents, such `as phosphatides in quantity ranging from 0.0003 to 0.004%by Weight of'the suspension` system. The system further 4includes a catalyst preferably of the peroxy type, such as diben'zoyl, `ditertiary butyl benzoyl,`

dicaproyl and dilauroyl peroxides and similar known peroxide catalysts. Such catalysts are used in quantity up to about 1%, most usually ranging `from about 0.1 to 0.5% by weight of the monomer.

A,'llie lsuspension system, as yfurther described in the White application (below), can further llaveadded thereto various quantities of `acids and buffering salts, `for instance, acetic acid, acetatesalts usually of the alkali or alkaline earth metals. various chaintransfer agents such as small quantities of mercaptan, for instance, `dodecyl mercaptan to `vary the mole-cular weight of the polymer, colors,stabilizers` and other `auxiliary agents commonly useful with theV bead polymers.

The present system contemplates the polymerization of'v vinyl aromatics suchas' styrene, however, `the polymerizartion of any suspension polyme'ri'zable ethylenically un'-v saturated monomer', such as alkyl Sty'renesjfor example, methyl and dimethyl styrene, halo genated styrenes,` for example, `2-cl'llorostyren'e, vinylpyridine, `divinyl-benzene and the like, is effected bythe method of this invention.

Further suggested has` been;`

butadiene/styrene copolymer, for example, GRS rubber, dissolvdin styrenevmolnomer. Other typical synthetic rubber :polymers that may be dissolved in `the liquid monomer yare polybutdien, c(')polyinersA of butadiene and ac'- rylonitrle andcopolymers of butadiene with isobutylne.

A typical water soluble `surfactant `is the alkalimetal salt of an' alkyl sulfate ester-'having' about 5 to` 9 carbon atoms such ras sodium octyl4 sulfate, but others, like so diumcapijoyl sulfato, lmay be used. s Asthe phosphatide when used, we` preferlcithin as described and claimed in a oopending applicatioh of Roy A. White, also assigned Deeembe 19',` .1958. y t Overall theprovblem ofi suspension polymerization has devolved .to2 eiecti'v lcoi,itn'uous polymerization `of the to applicants presentassign'ee, Serial No'. 781,441, led

liquidpolymerizablematrial suspended by agitationlin' waterltogethier accurately proportioned and distributed dispersing' agents, extender, catalyst and other necessary elements ora suspension system, as listed, to establi'sh maintain such systejrnnwherebythe particles poiym'eize as sneu inte here beide Witheet eeeleseing info large fmassesat. ystageV of thev ijlolymerization,` v For instance, sometimes'uduring' the reaction atearly stages, where .the raw material is monomeric or low 'molecular polymer', coalesoing takes place of semi-solid oiliquidlpartifcles the `coalesced product collects about @ne stirring" une 4feel-Laing what te; knows es s louipopsxf a large esoft'low molecularweight' polymer mass @highlyltackyw ch clin-gs to the `stirrer. Such mass whenr once formed or" begun to yform in the suspension system,

ldesthrloysm-all possibility of produciiigpolymer lb d's'in that,

course, canl `formataii'y` stage intermediate to the prokmolecular weightr polymer or relatively hard polymeric bead1 material.

On the` other hand, somet' reaction, that isi, after relativelyhard'polynier Ibeads-have sich, Suspension ,Systeem ClQSly 0fitf011dY iii' the rangesoperated within the conti-olrange as taught in `the atta Neverthelesslit'is mourn experience that `even operating foundmost o f wthe time to bensuccessfjul in the art, wil1 produce a Asubstantial number of ybatches of lollipop` at some intermediate stage whereby each such batch is lost; andalso` will'ofttimesin'nal `stages produce su-gar clumps. of" hard. granular 'bead polymer masses which e also'resul-t in failiire of the batch, again, even when `fol` art., f

Wehave' foundthat if the total reactionis controlled to'a'gradually descending pH curve asthe polymerizalsainted Aug. 13, 1963 u d l l M meeeeeeieseiiig eipftiuee' takes .place near the termination of the polynlerizationA We have 'further discovered that if, during the early or intermediate course of the reaction, such 'as up to about -four hours in a usual polymerization suspension system, the polymerization appears to be inhibited `and the reaction is not proceeding normally, -that fact will appear on the pH curve, the slope changes, definitely indicating de-v parture of the reaction from the normal, and that suspension is in danger of a lollipop forming and the suspension batch will usually be lost in a reasonably short time -following the break in the pH curve, unless corrective measures are immediately taken. Such corrective measures, we have found, comprise addition of a small amount of additional catalyst to speed up the reaction. It p may also comprise addition of an Iagent suicient to adjust the alkalinity or acidity of the reaction medium, to bring its pH toabout what the normal pH ofthe system should be at that point of the reaction. It may and preferably does comprise both addition of catalyst and adjusting of the pH.

After a substantial intermediate period of reaction time, about 21/2 to 6 hours, hard bead-like polymer will normally have formed. The pH at rthat point has reached a low sometimes below 6, sometimes about 5.5 or less. lf the lpH is `allowed :to continue to Ifall below about 5.8, it is Afound that the bead-like polymer, slightly tacky, will coalesce into granular clusters, comprising sugar clumps, a loss of suspension. Again, while we do not wish to be limited by ltheory, at the very low pH it is believed 'that the basic phosphates, produced ultimately by the hydrolysis of the phosphate as the reaction proceeds, and at la temperature labove about 70 C., become soluble or change its suspended strate in the `system at below about the critical pH below about 5.8. Thus, no insoluble (or properly suspended) phosphate particles are available at such low pH to maintain and prevent the slightly tacky polymer beads from coalescin'g into sugar clumps'. In any case, and according to a further aspect of this invention, the system is prevented from going below about pH 5.8, land generally when the suspension system, after several hou-rs of reaction', `has dropped in pH as low as about 6r, it can be quenched, that is, lan 'alkaline inhibitor is added -to prevent fthe system from going to a lower pH such as by addition of -any alkaline salt, for instance, lime or lime salts. l

For this purpose, as the-polymerizationhas proceeded for several hours, a pHlbelow aboutl 6, such las 5.8, is reached and hard tacky evenly suspended and substantially polymerized `granules! have been produced' in the suspen sion system, lthe system islbuffered; or the further arcidiic-ationris inhibited by- -additionof any type of alkaline substancepreferably lime or other alkaline salt, in small quantities TheA alkaline materialisadded' in` quantity of strength only suilicienrt to maintain the pH in or slightly above the range of 5.8 to 6.0. The system is alkalinized, at least to prevent it yfrom becoming more acid. Th-art addition of alkali may be in` the form of adding to the suspension systemfenough alkaline material such aslime or ammonia, to raise the pH above 6. It mayY be by addingonly smallquantities of such alkaline solution at a pHl of 5.8 to 6, allowing the polymerization to proceed, and then after a short period, ifthe pH tends togo lower, adding more, continuing -check-ing the pH of the system to note Whether ithas remained relatively constant,and adding more alkali only when the pH tendslto go lower.

Accordingly, it` will be noted :thatt-his invention com prises a method ofwcontrolling production of suspension polymer relatively secured #against inexplicableaillures by a pHand catalyst control. That control amounts to carrying ont the polymerization reaction in the presence of submicron sized phosphate particles, preferably hot precipitated in'situ art-high tempenatures, while constrainingr the suspension system to la relatively standardized pH- time profile curve for the system through allstages uof the reaction. Whenever, according to this invention, it is apparent Ithat thepH of the system departs fromxthe relaabout 5 .8 during 4the iinishing. ,p

. Y The invention is further explained with reference to the attached drawings wherein,

FIG.- 1 is atypical pH-time profile curve, an average of manynormal batches;

FIG. Z illustrates two typical departures at .intermediate polymerization stages front the relatively standard pH- t-ime profile of FIG 1,y presaging failure of each batch;

PIG. 3 illustrates lowering ofpH with temperature of a suspension system in a high pH curve where the pH loweringis progressiyeand an intermediate pH curve where the pH fallshrapidly alt about C.; 'andA FIG. `t illustrates the contrast in pH-tirne` curves of successful inhibitions by control of the pH in the region of 5r-8 to 6, and failures yby sugar clumping at pH below 5.8. A- normal suspension system, as the term is used herein, comprises a suspension` of polymerizablc substance in V water, usually in ratio ofy 0-.9 4to `1.1 of .polymerizable substance to 1 `o l water. Such system contains finely divided submi'cron sized phosphate particles of the group consisting ofoalcinm, barium andl magnesium in variably small quantities, up to about' 5% by weight of the suspension system, `an- `arr-ionic surfaceV active agent from about 0.0005% to 2% peroxy catalyst up to about 1% and minute quantities of other minor components. S-ueh normal; system, over a large number-of normal properly conrtrolled suspension polymerizations, produces a pH-time prolile 'curve las illustrated in FIG. `1. These systemsare operated over a wide range Aof temperatures" from about 404100?` C.r 'llhe systems may further indefinitely contain small quantities of aceticracid or such buite-ring salts as acetates, and phosphatides. Sometimes the system is set up by adding the finely divided preformed phosphate particles t'o `thel suspension-rand sometimes, according to another aspct of thisinvention; the phosphates are formed in suspension by =hot` precipitation, atv a temperature of '9D-100 C., of soluble phosphates with limeor other alkaa lineearth `rrnetalrhydroxide soluble ,salt .to form the insohlble phosphate particles in situ inthe system.

Such normal suspensionI system, as thus defined, most often gives'asuccess'ful` polymerization to'produce beads inY atypicalv pH-time cur-ve as`v shown by FIG. 1. However, a -largepercentargeof bead polymerizations attempted in normal suspension systems withinthe limits given above, fail 4for" reasons not known; Typical failures, however, are found according to this invention, to be pre# ceded by a'fbr'eak ir the normal cur-ve f pH vs; time vas illustrated in the several curves of the drawings, particularlyFIGS. 2 and 4. According'to this invention therefore, those failures can be prevented bykaddition of small quantitie's'of alkaline nia't'e'fials; added'at the proper `time "i ysf'erri" mal-curve. Since, las shown been @anfapparent lag in .the plyineiizationwher y .thep-H did not drop as expected-bythe normal pro ecu-rye, RIG. 1, it is also Offen desirable .t0 'add' mi@ analyst. .fg .accelerate th' polymerization slightly. AWlrelfthe .pH of a normal suspension systemn apparsiat `ari intermediate stage Ito depart nrom the-usual profile curve, FIGi 1, small quantities, usually lessd than `01.1%byweightof the systernofV peroxy catalyst are added.' Further test of the pHI of rthe adjusted-system will show whether the normal` pljlvto` be expected has been achievedf If` not, additional quantities ofcartalystand' sometimes small quantities ofacetic acid are added. When the curve appears to be normal, polym` erization will continueV andthe expected failure have been avoided forthatsuspensionbatch.- f

v Inl the region of the end point of the polymerization, that is, after about 3-4 hours reaction, as seen inthe curve', FIG. 4, the pH of the curve will have dropped to about 6, andV will tend to descend `below 6 and even below"5.5I =as shown in FIG. `14C. That polymer can and will usually clumpinto hard granular masses if the v pH is allowed to fally below .5, and often will, even when the pH goes below 5.8. ,'Ihis, fas pointed out and illustrated in FIG. 4H, is overcome by adding alkaline material, such as lime or other alkaline substances, dilute caustic, Iarrnnoniaor alkaline' salts, like sodium acetate or sodium phosphate whenever the pH goes as low :as 5.8. A -For instance, when ythe pH is raisedor held by addition of Ialkali afs in .thehidotted Iline curve ofl FIG; 4H, no sugar clumping of granulesfocours. VvFIG. 4G illustrates a typical drop of pH, near theend point, below 5.5, and the vfailure of a hatch by formation of sugar clumps. Curve 4H shows how the addition of alkali, lraising the pH slightly prevents sugar clumping. As indicated, no reasons fully explain the occasional batch failures. The continuous drop in pH by hydrolysis of phospate and production of phosphoricilaoid vis a partial explanation.

FI'G. 3F shows, at high initial `alkalinity of a system, at

pH about l0, that the pH -Wi-ll drop rwith rising temperature. Neventheless, no sharp break in the curve appears.

However, at more moderate initial alkalinity of the system,about 8, the pH may :drop very abruptly at temperatures above 70 C.,rand, las,v there illustrated, the pH may go mueh lloweriin an unbutleredfsystem with temperature rise. Y C t v Ina typical polymerization in a suspension system,` if the phosphate is a soluble phosphate like that of an alkali metal to be precipitated, the soluble saltA of the precipitating metal i.e. a soluble salt of the alkali earth metal, is added as a dry solidor as a solution in a small aliquot portion of the water, added with agitation grad- Y ually, whereby the hydroxy phosphate of the alkali earth metal is formed in small particles in the agitated aqueous medium. Thereafter, mostjof'l the monomer is added as the agitation is continued andnally'the remaining components, such as the phospholipid, the peroxy catalyst and acetic acid or acetate salt is added with agitation. 'Ille heating of the suspension system, while it may be applied from early stages, actually needs to be applied only during the actual polymerization with' agitation so that the heat may-take'place after the suspension system is established withagitation. The agitation at a desired temperature is continued until the `bead-like polymer particles are formed as a suspension in the agitated liquid overa polymerization p`eriod,.as needed, usually about 6 to 20 hours. Some of lthe conditions may be varied with the characteristics of theparticular monomer being polymerized as Will appear from the specic conditions set forth in the following examples:

vvThe invention is illustrated by the following examples:

Example I Parts (by weight) Water f 5000 Calcium chloride (CaCl2.2H2O) 1 29 Trisodium'phos'phate `(Na3PO4.l2H2O) 39.5 Sodium octyl sulfate t 6 Styrene monomer 5000 Benzoyl peroxide 11.6

Lecithin In setting up this batch, 4500 parts of water are charged to a reactor, and the trisodium phosphate and the sodium octyl sulfate are added and dissolved with agitation. The calcium chloride is dissolved in the remaining water and this solution is gradually added to the reactor with good agitation. A tine dispersion of calcium phosphate is obtalned. That agitation is then stopped and 4500 parts of styrene monomer are added immediately followed by the remaining 500 parts styrene in which the lecithin, and thebenzoyl peroxide have been dissolved. Agitation is again `started and homogeneous dispersion is obtained. The pH on starting was found to be about 8.5. The temperature is gradually increased to within an hour and also `maintained at this level with continuous agitation as the polymerization reaction proceeds. The pH descended rapidly reaching about 6.5 at the end of an hour. The batch was then split into two portions.k

in one portion, used as control, the agitation was continued, vthe slope of the curve decreasing whereby the further lowering of the pH almost ceased; in fact, the pH rose slightly. At the end of two hours the polymer and some monomer had begun to coalesce and deposit upon the agitator as soft tacky liquidforming a typical lollipop indicatinug loss of suspension and failure of the control batch. The pH curve of that control batch is illustrated in FIG. 20.

The other portion of the'batch hasV added thereto a small additional quantity yof 0.5 part by Weight of benzoyl peroxide. The pI-I then began to fall rapidly at approximatelythe original slope over a period of about 3 hours, reaching a minimum of 5 .8. At the end of this period 0.5 part :of powdered lime was added yand the pH rose to 6.3. The polymerization was continued at a pH of about 6.2- 6.3 as shown in FIGURE 4H for a period of about 7 hours. Analysis indicated that good polymer beads had formed at the end of 6 hours, analyzing 96.2 complete polymerization. Y At the end of 7 hours the system showed 97.5 polymerization and at the end of 8 hours upon terminatiom the 'beads indicated 98.4% polymerization; The polymer slurry containing the bead-like styrene is agitated toga pH of 3 with hydrochloric acid and centrifuged. t

After washing and drying, the product is a clear, non tacky bead-like material of which 90% by weight passes through a 40 mesh Tyler standard screen but remains on a 460 mesh screen.

- Example II The following formulation may be used for preparation of a styrene acrylonitrile copolymer:

Parts (by weight) The suspension of phosphate particles in water was iirst prepared as in Example I. The styrene and acrylonitrile were then added with agitation and finally small quantities of styrene in which the lecithin and peroxide had been dissolved were added. The initial temperature was 40 C; The temperature was allowed to increase to about 70 C. in the first hour. The initial pH Was 7.4 and this gradually dropped over a' period of 6 hours to about 5.5, the temperature then being gradually raised to about C. At this'point the batch was divided into two sections, therst remained as described as a control, and the second having added three parts of calcium hydroxide to slightly raise the pH to 5.8 with continued large sugar clumps. The alkalinized batch was acidiedto a pH of 3, centrifuged, washed and dried as in the preceding example, to obtain clear hard bead-like styrene acrylonitrile copolymer with high impact strength.

Example III Parts (by weight) zoyl peroxide and the acetic acid have been dissolved.A

Agitation is started and a homogeneous dispersion is soon obtained, At the end of 6 hours the batch was di-.

vided evenly into a control and an experimental batch. The temperature of each was raised to 95 C. with continued agitation. The control batch pH following curve FIG. 4G reached a level of about 5.3` and sugar clumps began to coalesce, that is,` particles of beads iloated to the top of the system in large clumps of hard granules which adhered together. In the separatedy experimental batch, when it has reached a pH of 5.7, 1.0 part of concentrated ammonium hydroxide was added which raised the pH to about 6.2 so that with continued heating and agitation the pH had descended no lower than about 5.8 at the end of ten hours. The experimental batch was acidiied with hydrochloric acid to pH 3 and centrifuged, as in previous examples, and clear dry styrene beads were obtained.

Example 1V A suspension system comprising 8000 parts water, 5.5 parts calcium chloride, 71 parts trisodium phosphate, 6.5 parts sodium octyl sulfate, 4600 parts styrene monomer, 400 parts butadiene/styrene copolymer (75:20) and 18 .parts benzoyl peroxide were charged to the reactor with continuous agitation, first adding 7500 parts of water, then the trisodium phosphate. The phosphate solution was heated to 90 C. with agitation and then the calcium chloride and sodium octyl sulfate, dissolved in the remaining 500 parts of water were added to form a finely divided suspension of calcium hydroxy hexaphosphate. 400 parts of well washed 75:25 butadiene/ styrene copolymer (emulsion polymerized at low temperature) in 4400 parts of styrene monomer in which .the 'benzoyl peroxide is dissolved and slowly added to the agitated phosphate suspension over a period of a half hour with good agitation, gradually increasing the temperature to about 100 C. The polymerization started at a pH of about 8 and gradually descended to about 6 in an hour following a curve as shown in FIG. 2D, at which point the slope of the pH curve leveled olf sharply to horizontal, rising slightly over the next hour. After two hours the batch was ydivided into a control portion and an experimental portion. For the control portion the agitation and heating was continued. The pH gradually dropped as shown in that curve with the polymer beginning to coagulate upon the agitator, gradually forming a large polymeric soft lollipop, thereby terminating in an unsuccessful batch. After the same two hour period, a further quan-- tity of 0.5 part of lbenzoyl peroxide was added to the agitated experimental portion over a period of minutes and the pH'slowly dropped to about 6, and the polymerization was then continued over a .period of 12 hours.

reaching a minimum pH of 5.7. After 15 hours the polymerization was terminated. The bead slurry was acidied to the pH of 3, centrifuged and the polymer beads were washed and dried showing clear resilient beads of good impact strength.

Example V Parts (by weight) Water 5000 Calcium chloride (CaC12.2H2O) 28 Trisodium phosphate (Na3PO4.12H2O) 39 Sodium octyl sulfate 6 Styrene monomer `5000 Benzoyl peroxide 12.4 Lecithin i 0.047 Acetic acid 0.29

4000 parts of water are heated to boiling and thereafter a boiling solution of 39 parts of trisodium phosphate and 6 parts of sodium octyl sulfate in 500 parts of water, is added to the first boiling batch with agitation and forms a clear homogeneous hot solution. Thereafter 28 parts of calcium chloride (CaCl22H2O) dissolved in 500y parts of water, heated to boiling, is slowly added to first the agitated :boiling solution of trisodium phosphate over a period of a half hour, and the agitation is continued for an additional half hour. Thereafter, 5000 parts of styrenemonomer having 12.5. parts of benzoyl peroxide and 0.05 part of lecithin dissolved therein are slowly added to the i hot agitated suspension.' The beads formed, following the procedure of Example` I, were` found to have a relatively constant particle` size in the range of 40-60 mesh.

Example VI Procedure of Example V was repeated except that the suspension of` calcium phosphate was formed in situ as described but at Aa temperature of 60?` C. It Was found that a substantially constant particle size bead of slightly larger bead particles having a screen mesh size of -100 were formed.

As thus described it has been found that a reliably good suspension polymerization follows the prole of curve as set -forth in FIG. 1 comprising a gradual drop of pH of the suspension system to a minimum of about 5.8, preferably in the range of 5.8 to 6.0, gradually rising thereafter. When a suspension polymerization reaction is regulated to follow such normal reaction curve, good, nontacky strong transparent polymer beads are formed. Where in a normal suspension polymerization system a break in the pH-time profile curve appears, that break is clear indication that there is some fault in the polymerization. If that reaction is allowed to continue unchecked, the polymerization will 'be defective, lollipops will form at an intermediate stage, or sugar clumping will occur after bead granules are formed. However, if corrective measures are applied where a break in the curve appears, that batch can be saved. It is usually savedby measures applied prior to substantial coagulation of the suspension. The procedure involves rst correction of the pH to that approximately normal for the curve, usually by addition of more catalyst to accelerate the polymerization.

Again, during the iinal finishing stages of the polymerization and when substantial polymerization has been effected whereby the product is substantially polymerized into beads, the -beads may be tacky and tend to coagulate and adhere into sugar clumps at a pH below about 5 .5 It is found that this may be prevented by addition .in the nal polymerization stages, of an alkaline substance t0 prevent the pH from going below 5.8, in quantity either to inhibit the lowering of the pH below that critical limit to stabilize it in the range of 5.6 or to slightly raise the pH.

In a preferred procedure, it is found that the polymer beads lmay be produced in more constant particle sizes by forming ne insoluble phosphate particles by precipital tion in situ from hot solution of reagents to form the 1 1 insoluble phosphate at a high temperature in the Yrange of 90-l00 C. f

We claim: l

l. In the suspension polymerization of styrene monomer catalyzed with a peroxy catalyst by agitation of a suspension of the styrene catalyzed monomer in Water to form an agitated suspension of small liquid droplets which sometimes tend to coalesce into a large partially polymerized .mass atan intermediate stage of the suspension polymerization, said tendency to coalesce being indicated further by an abnormal rise in pH of the suspension polymerization system, the step of adjusting the pH of the suspension system to a condition yapproximately normal for this suspension polymerization Vsystem when compared toanaverage pHtime prole curve having the formillusnated inFIG. 1, said adjustment ofthe pH being effected by adding to the suspension system a quantity Vsutiicient to effect the necessary pH reduction of `a substance selected'from the group consisting of an acid, a peroxy catalyst and both an acid and a peroxy catalyst.

2. In the suspension polymerization of a liquid'solution 4of syntheticrubber consisting essentially of Ia copolymer iof butadiene and styrene,vdissolved in styrene monomer catalyzed with a peroxy catalyst .by iagitati'onaof a suspension of the styrene catalyzed monomer in'vvater t0 formv an agitated suspension of small liquid dnoplets which sometimes tend to coalesce into a large polymerization, Y

said tendency to coalesce being indicated lfurther by an abnormal risehin .pH ofthe suspension polymerization system, lthe step 'of adjusting the pH of the suspension system to a condition approximately normal 'for this suspension polymerization system when compared to an average pH- i time profile icurve having the form illustrated in FIG. 1,

said adjustment of the pH being eected by adding to the suspension system a quantity suflicient to effect the necessary pH reduction of a substance selected from the group consisting of an acid, a peroxy catalyst and both an acid and a peroxy catalyst,

41, pages 1021-4'(1949).

3. In the suspension polymerization of a liquid solution of poiy-acrylonitrile dissolved in styrene monomer catalyzed With a `peroxy. catalyst by agitation of -a suspension of the styrene catalyzed monomer in Water to [form ian agitated suspension of small liquid droplets which sometimes tend to coalesce intro a large partially .polymerized `mass at an intermediate stage of the suspension polymerization, said tendency to Icoalesce being indicated further by an abnormal rise in pH of the suspension polymerization system, the step of adjusting the p'H of the suspension system to` a condition lapproximately normal for this suspension polymerization system when compared to an average pH-time profile curve having the form illustrated in FIG. l,` said adjustment Kof the pH being effected by adding to the suspension system a quantity sufficient to effect the necessary pH reduction of a lsubstance selected from the group consisting of an acidaV peroxy catalyst and both an acid and a peroxy catalyst.

References Cited in the le of this patent UNITED STATES PATENTS OTHER REFERENCES Marvel et als' Journal American Chemical Society, vol. 72, pages 5026-9 '(1950).

Gould et al.: Industrial Engineering Chemistry, vol. 

1. IN THE SUSPENSION POLYMERIZATION OF STYRENE MONOMER CATALYZED WITH A PEROXY CATALYST BY AGITATION OF A SUSPENSION OF THE STYRENE CATALYZED MONOMER IN WATER TO FORRM AN AGITATION SUSPENSION OF SMALL LIQUID DROPLETS WHICH SOMETIMES TEND TO COALESCE INTO A LARGE PARIALLY POLYMERIZED MASS AT AN INTERMEDIATE STAGE OF THE SUSPENSION POLYMERIZATION, SAID TENDENCY TO COALESCE BEING INDICATED FURTHER BY AN ABNORMAL RISE IN PH OF THE SUSPENSION POLYMERIZATION SYSTEM, THE STEP OF ADJUSTING THE PH OF THE SUSPENSION SYSTEM TO A CONDITION APPROXIMATELY NORMAL FOR THIS SUSPENSION POLYMERIZATION SYSTEM WHEN COMPARED TO AN AVERAGE PH-TIME PROFILE CURVE HAVING THE 